Conventionally, in a typical vehicle wiper apparatus, the rotation output of a motor rotating in a certain direction is converted into a reciprocating movement by means of a link unit so as to reciprocate a wiper arm (hereinafter, sometimes referred to merely as “arm”) on a surface to be wiped (e.g., windshield). In recent years, along with a requirement to narrow down the attachment space of the wire apparatus, a system that drives a wiper arm by a forward/reverse rotation of the motor has been developed in order to reduce the movement area of the link unit to less than half that of a conventional link unit and has been adopted in many cars.
In a wiper system that forwardly and reversely rotates a motor, the movement area (working limitation) in the up-down direction is limited by a mechanical stop. On the other hand, the reciprocating movement of the arm is realized by switching the rotation direction of the motor at the timing when the arm reaches the upper and lower turning positions. Therefore, in controlling the motor drive control, it is necessary to detect whether the wiper arm has reached the turning positions in the motor drive control. To this end, the position and movement speed of the wiper arm need to be detected. For example, in a system described in Patent Documents 1 and 2, the position and the movement speed of the wiper arm are detected by means of a motor rotation pulse generated in association with the rotation of the motor.
FIG. 7 is an explanatory view showing the basic configuration of a motor unit 50 used in the wiper system that forwardly and reversely rotates a motor. As shown in FIGS. 7 (a) and 7 (b), in this wiper system, a multi-pole-magnetized magnet 53 having a plurality (e.g., six poles) of magnetic poles formed in the circumferential direction is fitted to a rotary shaft 52 of a motor 51. Further, a magnetic sensor 54 such as a Hall IC is arranged opposite to the multi-pole-magnetized magnet 53. When the motor is driven, the multi-pole-magnetized magnet 53 rotates with the rotary shaft 52 of the motor and the polarity of the magnetic pole located opposite to the magnetic sensor 54 changes accordingly. A sensor signal as shown in FIG. 7 (b) is output from the magnetic sensor 54 each time when the polarity changes and the output signal is input to a control unit so as to be used as a motor rotation pulse.
There exists a correlation based on the reduction ratio or link operation ratio between the rotation angle of the rotary shaft 52 and movement angle of the wiper arm, so that it is possible to calculate the movement amount of the arm from the rotation angle of the rotary shaft 52. Thus, the position of the wiper arm is detected by means of additions and subtractions of the number of motor rotation pulses. However, since there is a risk of pulse shift when relying only on motor rotation pulses, a magnetic sensor 55 serving as an absolute position detecting sensor is added to the wiper system and the pulse count is corrected by the output signal of the sensor. For example, a position detecting sensor is arranged near a storage position of the wiper arm and the pulse count is reset to a predetermined value when the output signal of the sensor is obtained in order to recognize the position of the wiper arm by the number of pulses counted from the absolute value.
As shown in FIG. 7 (a), in the wiper system, a ring magnet 57 is fitted to a worm wheel 56 engaged with the rotary shaft 52. The ring magnet 57 has two magnetic poles formed in the circumferential direction and rotates with the worm wheel 56. As shown in FIG. 7 (c), a sensor signal is output from the magnetic sensor 55 when the magnetic pole of the ring magnet 57 arranged opposite to the magnetic sensor 55 changes from N pole to S pole. Then, as shown in FIG. 7 (d), by counting the number of motor rotation pulses with the sensor signal output position set as the original point position, it is possible to detect the movement of the wiper arm from the original point position. With the pulse count corresponding to the turning positions previously calculated and set, the motor is reversely rotated when the pulse count reaches a predetermined value, whereby the wiper arm is reciprocated between the upper and lower turning positions.
In the normal operation of such a wiper system, the original point position is recognized in the first wiping operation activated in response to turn-on of a wiper switch. FIG. 8 is an explanatory view showing original point position recognition operation performed at the start-up time. In a switch-off state, the wiper arm is situated at the storage position, and the state of the ring magnet 57 at this time is as shown in FIG. 8 (a). That is, N pole of the ring magnet 57 faces the magnetic sensor 55, and the sensor signal thereof is in a High state. When the wiper switch is turned on in this state, the motor 51 drives in the backward path direction (direction from upper turning position toward lower turning position). Then, ring magnet 57 rotates leftward as shown in FIGS. 8 (a)→(b) and the original point position (boundary between N pole and S pole) reaches the position corresponding to the magnetic sensor 55. As a result, the sensor signal changes from High to Low state, whereby the original point position is recognized at the wiper start-up time.
However, when the wiper arm is stopped at a position below the original point at the wiper start-up time, the magnetic sensor 55 is situated in the S pole area. Thus, even though the motor is driven in the backward path direction, the N/S boundary does not face the magnetic sensor 55 during the abovementioned operation, with the result that it is impossible to recognize the original point position. Further, when the arm is situated at a position near the upper turning position of the wiping area, the magnetic sensor 55 is also situated in the S pole area. In this case, however, the original point position passes through a position corresponding to the magnetic sensor 55 by the abovementioned backward path movement at the start-up time, whereby the original point position can be recognized.
In order to cope with the above problem, when the arm is situated at a position below the original point position, the motor 51 is driven in the backward path direction and, then, the operation of the motor is controlled with the lower limit position at which the motor is locked set as a reference position. The control operation at the wiper start-up time is shown in a flowchart of FIG. 9. As shown in FIG. 9, when the wiper is turn on, the motor drives in the backward path direction as described above (step S51). The flow advances to step S52 where it is determined whether the motor 51 is in a locked state. In the case where the wiper arm is stopped at a position below the original point position (i.e., position between the original point position and lower limit position), the wiper arm reaches the lower limit position by the movement in the backward path direction and is then brought into contact with a mechanical stop. As a result, the motor 51 is in a locked state, and this locked state is detected in step S52.
The lower limit position is an absolute position that has previously been set. When the state where the wiper arm is situated at this position can be recognized, the current position of the wiper arm can be calculated by performing pulse count starting from the lower limit position as a reference. Thus, when it is determined in step S52 that the motor 51 in a locked state, the flow advances to step S54 where wiping control is performed based on the pulse count. However, also in this case, the pulse count is not performed starting from the proper original point position, so that it is necessary to correct a count value in course of the wiper arm operation. FIG. 10 is an explanatory view showing pulse count correction control after the motor lock.
As shown in FIG. 10 (a), when the motor 51 is in a locked state at the lower limit position by the movement in the backward path direction, the counter is once reset at the lower limit position as an original position. Afterward, as shown in FIG. 10 (b), the motor 51 is driven in the forward path direction (direction from lower turning position toward upper turning position) and, at the same time, pulse count control is started. Along with the movement of the arm, another N/S boundary of the ring magnet 57 reaches the magnetic sensor 55. This N/S boundary also faces the magnetic sensor 55 at the time when the wiper arm reaches a predetermined position. In this system, therefore, the predetermined position is used as a check position and, as shown in FIG. 10 (c), when a signal indicating that the magnetic sensor 55 faces the check position is obtained, the pulse count value is corrected to a previously set value. Thus, even in the case where the arm position is recognized by a motor locked state, normal pulse count control can be restored by the correction based on the check position.
On the other hand, when it is determined in step S52 that the motor 51 is not in a locked state, the flow advances to step S53 where it is determined whether the original point position has passed the magnetic sensor 55 (i.e., whether the magnetic pole is changed from N pole to S pole). When the original point position has not passed, the flow returns to step S51 where the movement in the backward path direction is continued to repeat the processing of steps S52 and S53. When the wiper arm is stopped at a position above the original point position, the original point position reaches the magnetic sensor 55, and it is detected in step S53 that the original point position has passed the magnetic sensor 55. In this case, it is determined that the wiper arm reaches the original point position, the backward movement is then stopped, and the flow advances to step S54. In step S54, wiping control is performed using the pulse count based on the original point position, whereby the wiper arm is reciprocated to perform wiping operation between the upper and lower turning positions.
Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 11-301409
Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 2004-274804
However, in such a wiper system, when an obstacle 62 such as snow exists on a windshield 61 as shown in FIG. 11 (a) and a wiper arm 63 is stopped in the middle of the wiping operation, the following problem arises. When the wiper switch (or ignition switch) is turned off in the state shown in FIG. 11 (a), the arm position information (pulse count value) obtained up to this time is reset. Therefore, at the wiper restart time, the processing shown in FIG. 9 is executed so as to recognize the original point position and the like (original point position and arm current position detected based on the contact state to the lower limit position when the arm is stopped at a position below the original point) of the wiper arm 63.
In this case, if there is no obstacle 62 and the wiper arm 63 can freely move in the backward path direction, the original position and the like of the arm is recognized by the control operation shown in FIG. 9 at the start-up time and normal pulse count control can be restored without problems. However, as shown in FIG. 11 (b), when the obstacle 62 interferes with the return of the wiper arm 63, it is determined in the processing of FIG. 9 that the motor is locked at this moment and, accordingly, the flow advances from step S52 to step S54. In particular, in the case where the arm is stopped in the S pole area above the check position, there is no chance of detecting the arm position other than the arm lock state. Thus, the lock state caused due to the existence of the obstacle is determined as the arm lock state in step S52. That is, the stop of the wiper arm 63 due to existence of the obstacle 62 may falsely be recognized as the stop of the wiper arm 63 at its lower limit position and, in this case, the pulse count control is started at the falsely recognized stop position.
When the pulse count control is started based on the motor lock caused due to the obstacle 62, the wiping control is executed in a state where the pulse count value and actual arm position do not coincide with each other. Thus, even though the wiper arm 63 actually reaches the upper turning position, it is recognized that the wiper arm 63 is in the middle of the forward path in the control, so that the wiper arm 63 is not stopped. Accordingly, the wiper arm 63 continues moving in the forward path direction with the result that, as shown in FIG. 11 (c), a wiper blade 64 may overrun and collide with an end portion 61a (A-pillar) of the windshield 61. When the wiper blade 64 overruns as described above, the wiper blade may be broken, or windshield 61 or A-pillar may be damaged. Thus, when the wiper is caused to operate in a state where the pulse count value and actual arm position do not coincide with each other as described above, the arm movement cannot appropriately be controlled.
An object of the present invention is to prevent a wiper apparatus from falsely operating in restart time even after occurrence of a problem in which snow or the like interfere with the movement of the wiper arm.